To develop fluorescent indicator dyes for the utilization of optical methods to determine airway surface liquid and other fluid composition by measurement of the emission of fluorescent indicator dyes for Na or Cl covalently attached to a large dextran molecule or latex bead. The ion indicators must change their fluorescence emission or absorption in proportion to alterations in the Na or Cl concentration of extracellular fluids, concentrations of about 150 mM. The indicator dyes should be excited by visible wavelength light, be water soluble, non-toxic, and minimally affected by the presence of proteins.